In order to solve the overcharge problem of the secondary battery, the commonly adopted solution is to cut off the main circuit of the battery before the electrode assembly fails so that the further charge of the electrode assembly will be prevented and then the secondary battery will be kept safe. Generally, an upper surface of the top cover plate is a flat surface, a through hole is defined through the top cover plate, and a deformable plate is welded to the inside of the top cover plate and covers the through hole.
In the related art, the secondary battery further includes a second terminal assembly protruding beyond the top cover plate, and the portion of the second terminal assembly beyond the upper surface of the top cover plate has a relatively great height. In order to facilitate series or parallel connection of the secondary batteries by using a current collection member after the secondary batteries are assembled into a module, a conduction block is generally used and, specifically, the conduction block is welded to the external side of the top cover plate and covers the through hole, and the upper surface of the conduction block is substantially even with the upper surface of the second terminal assembly. However, the conduction block is merely used for conducting electricity and filling the space between the upper surface of the top cover plate and the upper surface of the second terminal assembly (i.e., said space has poor utilization), thus, the energy density of the secondary battery cannot be further improved. In addition, the welding of the conduction block may generate residue welding stress that is applied to the deformable plate, which caused that the deformation force of the deformable plate deviates from a preset value, influencing the safety performance of the secondary battery.